Gaseous phase photohalogenation of hydrocarbons



Aug- 12, 1952 J. A. PIANFETTI ETAL -2560.63.67

GAsEous PHASE PHoToHALoGENATIoN oF HYDRocARBoNs Filed Sept. 16, 1948 IN VEN TORf` JIaH/v ,4. PMN/ferr; BY 9066er M mmfe/mw irren/5)!" Patented Aug. 12, 1952 UNITED .Partnr FFE GASEOUS PHASE PHOTOHALOGENATION F HYDROCARBNS Application September 16, 1948, Serial No. 49,622 claims. (ci. 20a- 163) This invention relates to the production of halogenated hydrocarbons by the direct halogenation of hydrocarbons and of incompletely halogenated derivatives thereof.

vDirect halogenation has heretofore been accomplished experimentally by three general methods, namely by thermal action, catalytic action and photochemical action. Commercialization of these processes has been prevented or Ahindered-byl reasonof a number of operational diculties. Thermal processes involve very high temperatures, explosive dangers and -diiliculties as to corrosion as well as to the avoidance of decomposition products or other undesired derivatives. Catalytic processes have the disadvantages of objectionably high temperatures, explosive dangers, inability to prevent, or complications in preventing, overheating of the catalyst in reactors operated at high enough capacity for commercial success, and nally the high expense of operation.

Photochemical chlorination processes, though capable of operating at lower4 and more easily controlled temperatures than the foregoing processes, have the disadvantages that if they are operated at a suiciently high capacity to be of .commercial interest, they not only involve temperature'regulation difculties but also produce reaction product gases containing free chlorine which chlorine decreases substantially the difculty of recovering the chlorinated hydrocarbons in bodies of acceptable purity.- In the chlorination of hydrocarbons such as methane for example, the photochlorination rate becomes extremely slow after about 90 to 95% of the chlorine has reacted. If the process were run at a'rapid rate thereby leaving residual chlorine in the chlorination products, such loss of chlorine to the reaction would make the operation inefcient. If the free chlorine were recovered for reuse, the cost oi such recovery would render .the whole process economically unsatisfactory.

An object of the present invention is to provide processes for the direct halogenation of hydrocarbonsvwhich do not involve the above described disadvantages and which are capable of operating at high throughput rates while at the same time producing halogenated hydrocarbon reaction products substantially free of halogen. Another object is to provide a halogenatipn process wherein the temperatures are suiiiciently low and the manner of handling the halogen and the hydrocarbons is such as will avoid excessive corrosion of equipment and as well will not involve explosive dangers. Still another object is to utilize reactors and other equipment for such process which are simple in construction and easy to operate. l More generally, the ultimate object is to provide low cost processes for producing any of a large number of halogenated hydrocarbons Yinvolving efficient utilization of the raw materials and equipment employed.. Among the hunted objects is one to provide a process capable of operation in such manner as to produce larger percentages of specifically desired halogenated hydrocarbons, such for example, as higher percentages of carbon tetrachloride from methane.

Broadly considered, the processes of the present invention involve a combination of photochemical halogenation followed b-y catalytic halogenation, al1 in the vapor phase. The reaction of the halogen With the methane or other compound is only partially completed by the action of actinic light rays and the reaction product gases including the unchanged reactants leaving the photochemical reaction vessel or reactor are subsequently reacted with the aid of a catalyst. Although elevated temperatures are employed in both reactions, they are moderate -and are suiiiciently low to permit avoidance of local overheating and to avoid decomposition of the reaction products and excessive corrosion of the equipment. The nal reaction product gases leaving the catalytic reaction vessel or reactor show substantially 100% conversion or consumption of the halogen. In View of this freedom '.from halogen, the gaseous reaction products may be condensed, collected and separated into their Ythe amount of halogen in the gases owing through the catalyst is comparatively low, thus restricting the amount of reaction and the amount of exothermic heat developed in the reactor. Furthermore, the high volume of reaction product gases produced in the photochemical halogenation and present along with the reactant gases in the catalytic halcgenator serves to absorb most or substantially all of the excess exothermic heat and to prevent any local overheating. Finally, high capacity operation is possible because catalytic halogenators of simple construction are used in which a porous bed of coarse catalyst is contained, permitting free flow of the gases.

In all operations of the process Vthe major part of the halogenation is brought about in the photochemical reactor or reactors and a minor part occurs in the catalytic reactor. In chlorination reactors, most efficient results aregenerally obtained when only about ten to'fteen' per cent of the initial chlorine is left for reaction Y Vthrough external walls or into -internal cooling tubes is required. rThe exterior Walls may" even' vibefirisulat'ed thereby toobtain increv uniform 'regulation of the temperature in the reactor.'l

In accordance with an important feature of the invention, the throughput rate at which the process is operated is increased by recirculating a partv of the reaction product gases through'the photochemical chlorinator o r chlorinators in whichlthe major'part of the chlorin'ationreaction takes place. Before they are reintr`oduced, lfthe 'Withdrawn'gases are cooled somewhat"butv preferably only to a temperature still sufficiently Y elevated to heat the reactant gases to the desired temperature for immediate rapid reaction-in the photochemical reactor. The recycled gas accomplishes a very successful regulation of the temperature in .the photocheniical chlorinator or chlorinators by absorbing the excess exothermic heat. vThe ratio of the recycled gases introduced into the chlorinator to the reactant gases Ais adjusted such that the temperature rise produced by the heat of the reaction is not great enough to' cause any decomposition of the chlorination products or great enough to cause excess deterioration of the apparatus. The recycling of the gases and their admixture with the reactant gases before the latter are exposed tov the actinic light or before they are heated to a high temperature serves the additional function of avoiding the formation of an explosive mixture.

In the preferred operation of the present invention, a vseries of photochemical chlorinators is employed in combination with a catalytic chlorinator. "Ihe particular number to be employed in the series to obtain most eiicientl resultsdepends upon the reactants, their ratio Withrespect to each other and the throughput capacity to be employed. In any case, this provision makes possible a greater throughput capacity than otherwise would be obtainable. In the treatment of chlorine withl methane in the molecular lratio of 3.5, a plant of the commercial capacity contemplated calls for nve chlorinators in series, which capacity or total amount of chlorination would require about twenty-inve photochemical chlorinators ii they were operated in parallel.

The process of the invention is of particular value for the halogenation of methane and other low-boiling hydrocarbons and partly chlorinated hydrocarbons. It is applicable generally for the treatment of the `same compounds to which photochemical and catalytic halogenatons have been considered applicable following procedures suggested in the prior art. Practically considered, the new process is especially suitable for halogenating hydrocarbons -of fivev orv less carbon atoms, but higher molecular weight hydrocarbons can also be reacted.

, The process is applicable to the halogenation of both saturated and unsaturated hydrocarbons, including-thev paraiiins, as for example methane,

"ethai'ie' and propane, the olens, as for example ethylene and propylene, the aromatics, the

. naphth'enesand the acetylenes, as Well as their derivatives. ,"IheA process may also be employed for the accomplishment of dehydrohalcgenation by which halogenated alkylenes are obtained and for the accomplishment of mixed halogenation reactions as with chlorine and bromine. Finally, the halogenation of propane or propene may be carried out in such manner that ssionof the carbo'nfcarbo-nfbond occurs at the's'ame'time,

-resuiungyinthg formation of mixed haiogenatd hydrocarbons as ch'lorom'ethancs, chloroethanes or chloroethylencs -which, 1 through exhaustive chlorination, may beinade to form carbon-tetrachloride and perchloroethylene. v

`The process of'the invention contemplatesreacting chlorine with methane in molar ratiosf'as low 'as 1 to 1 andas high as 4 'to 1. 'Il-'iefparticular ratio employedv toa' large extent determines the number-"of--ichlorine atoms introduced into the hydrocarbon molecules'. v

i For the chlorination of methane -the'preferred temperature for the operation of the pliot'ooh'emical chlorinatori'sinthe range -of '100 -to"f300 C. Temperatures'- asf-'lov'.r as 50' C. and a'shighv as 4 45" C. can be "employed, however, but -w'ithfless advantage; Althoughsomedecomposition cfthe reaction products occurs at temperatures above said range, under some circumstances temperatures as high as 600 C. may -be employed' Without excessive penalty. f y i' In operation'of the -catalyticchlorinator 4the preferred temperature is from 200"-to 400- C.f At suchtemperatures the chlorinator can be operated at suicientlyhigh capacity without-involving' dificulty of temperature control in the'catalytic bed. The catalytic reaction can be 'carried out at a temperature as low as 100 C., but the resulting rate o f reaction is ordinarily too slow for practical purposes. The temperature in the catalytic reactor may be permitted 'to rise to'as high as 500 but ordinarily control of the reaction at such temperature is too diicult, andundesired'reaction products are obtained. With suitable catalysts and high space velocitiesjtis possible to employ temperatures as high as 600 C. without causing excessive decomposition.

The foregoing temperatures applicablefto the chlorination of methane are also applicable'in general to other hydrocarbons and to partially chlorinated hydrocarbons. In bromination reactions the temperatures required are generally substantially lower. In any case the lowest temperature employable with any specific `operation of the process is that which brings about an acceptable rate -of reaction, and the highest temperature permissible is in general that which is just below that at which undesired decomposition becomes excessive. However', other factors such as corrosion difficulties, may dictate the use of lower temperatures than the theoretically permissible' maximums, in which case temperatures below about 300 C. may be required.

The process of the present invention may be advantageously carried` out in the apparatus illustrated in the accompanying diagrammatic drawing wherein the rst photochemical chlorinator and the catalytic chlorinator are shown in part in vertical section. With reference to the drawing, there are shown five photochemical halogenators or chlorinators IBa to Ie inclusive and one catalytic halogenator or chlorinator II, all connected in series. The chlorinators are constructed of lead, nickel or other material resistant to the corrosive action of the substances present. Each of the photochemical chlorinators is provided With a lamp I2 having therein a mercury arc or other source of actinic light. The said lamps are mounted in glass-Walled light wells I3. Each of the chlorinators IIJ is also provided with a perforated annular conduit I4 for discharging a cooling liquid upon the exterior walls. In connection with the chlorinators IIJa and Ib, the conduits I4 are optional and are not ordinarily required in view of the high efiiciency of the recycled gases hereinafter described in removing excess exothermic heat and controlling the temperature in the vessels.

In operation the methane or other hydrocarbon or chlorinated hydrocarbon is introduced through the inlet conduit I5 into the conduit I6 leading to a gas pump I I from which the methane flows through conduit I8 to the rst chlorinator I Ila. The chlorine or other halogen is introduced from a supply conduit I9 into the conduit I 8. The mixture of gases in this conduit I8 flows into the chlorinator Illa beneath an optional perforated false bottom 2l which serves to distribute the gas mixture and to suppress any burning tendency that might occur-before the reactants are fully diluted with the partially reacted gases in the reactor. The perforations are of small diameter and preferably of inch size. The reactant gases or either of them, in some instances, may alternatively be introduced at other points in the system as directly into the bottom of the reactor instead of into the conduits I6 and I8.

The reactants and reaction products pass upwardly through the photochemical chlorinator Illa and are there exposed to actinic light. They pass through the reactor at a rate which effects only partial reaction of the chlorine and the hydrocarbon. The reaction products and remaining reactants leave the reactor |311. through the conduits 22 connected with the single conduit 23 leading to the second photochemical chlorinator IBD. From this conduit 23 a portion of the eluent gases, and usually a major portion thereof, is withdrawn in conduit 24 for recycling leading to a gas cooler 25 (which may be a conventional heat exchanger) the outlet side of which is connected to the conduit IB leading to the conduit I8, into which conduits the initial materials to be reacted are introduced. The recycle gases mixed with the chlorine and methane gases serve to heat the same to the temperature required for the initiation of the photochemical reaction in the reactor I0a.

In some operations it is preferable to cool the effluent gas leaving the reactor Ia vbefore the same is introduced into the reactor IIlb. In this case the valve in line 23 is closed thereby causing all of the eiiluent gas to flow through the conduit 24 and cooler 25. Then part of the eiiluent gases to be fed to the second chlorinator Ib is taken o from the conduit I6 in the conduit 26 which connects with the line 23 leading into the bottom of the second photochemical chlorinator Ib.

Lll)

The reactor Ib may be identical in structure to the `reactor Ia and it is also preferably provided with similar means for recycling and cooling part of the eiiluent gas. Instead of employing a dual recycling system, a single system may be used in which the eiiiuent gases from the reactor Illb to be recycled are divided and part introduced into reactor Ilia and a part into reactor IIIb.

In the second reactor I0b an additional part of the chlorination is effected. The eiiluent gases still containing free chlorine and compounds to be chlorinated leaving the top of the second photo chlorinator, pass through the conduit 2I into the bottom of the third photochemical chlorinator Ic and thence through the fourth and iifth chlorinators IIlcZ and IIIe in the same manner as hereinbefore described.

In a typical operation, about 50% of the initial chlorine is reacted in the rst, and about 20% in the second photochemical chlorinator. In the last three photochemical chlorinators an additional 20 to 25% of the chlorine is reacted leaving from 5 to 15% of chlorine for reaction in the catalytic chlorinator II. In view of the limited amount of reaction to be effected in the last four chlorinators, recirculating and cooling circuits are not ordinarily required.

The efliuent gases leaving the fifth andlast photochemical chlorinator Ie in the conduit 28 ilows to the top of the catalytic chlorinator I I and thence through an insulated chamber 29 containing a suitable catalyst and out through the conduit 33. The catalytic chlorinator is provided with an optional circuit for recycling the eiiiuent gases, that is a conduit 3| interrupted by a gas cooler 32 and a gas pump 33. The presence and utilization of this circuit permits the system, if desired, to be operated such that a larger proportion of the chlorine can be reacted in the catalytic chlorinator and less in the photochemical chlorinator or chlorinators. The efliuent gases can be recycled in amounts to absorb the excess exothermic heat. In the runs carried out up to the present time, most efficient results have been obtained when the proportion of the chlorine left to react in the catalytic chlorinator has not been suiiicient to require recycling of efliuent gases to absorb exothermic heat. Y

In the operation of the invention absorptive materials such as active carbon and active charcoal are preferred. However, in its broadest aspects the present invention contemplates the use of other non-metal catalysts such as phosphorus trichloride and of metal catalysts such Vas copper and other metals which can combine with chlorine to form salts reducible by hydrocarbons to liberate hydrogen chloride. Since the rate, of reaction in the catalytic reactor used in the present process is slow due to the low percentage o-f free chlorine in the gaseous mixture, the space velocity must be low or the path of travel through the catalyst must be adequately long. As is shown in the drawing, a straight flow catalytic chamber of substantial length as compared with its cross section, will operate satisfactorily.

In the catalytic chlorinator II the remaining chlorine gas reacts with the remaining hydrocarbon or other chlorinatable material thereby providing substantially chlorine-free eiiluent gases in the exit conduit 30 leading to suitable recovery equipment usually including condensers and a Water absorber for hydrogen chloride.

If so desired, the complete reaction of the chlorine may be aided by the introduction of hydrogen or other readilychlorinatable material into the conduit 28vthrough the conduit 34, leading tothe catalytic chlorinator I l Furthermore.; the'invention broadly contemplates completion of the halogenation in a series of Ycatalytic or thermal halogenators as well as in a single such halogenator..

- Example 1 Into a system containing a single photochemical chlorinator connected. tov a` single catalytic chlorinator, both of the construction hereinbefore described but having no means for the recycling of gases, there was introduced chlorine and methane at the rates or" l1 pounds (0.155 mole) of the former and 0.7 pound (0.044 mole) of the latter perhoun'the same being directed into the bottom of the photochemical reactor. The temperature therein was maintained at approximately 305 C. maximum. In this chlorinator, the chlorine and methane reacted to provide chlorinated hydrocarbons leaving only to 11% of free chlorine in the eiliuent gases. These gases were then passed directly into and through the catalytic reactor containing activated carbon in which a maximum temperature of about 453 C Was reached. The nal reaction product gases from this unit contained no free chlorine and consisted principally of carbo-n tetrachloride (94% Vof the condensed liquids) together with smaller amounts of other chloro methanes, with hydrogen chloride and a-small amount of methane which escaped reaction.

Example 2 Into a system similar to the foregoing but containing the recirculation conduits, the pumps and cooling equipment hereinbefore described, pounds of chlorine and 4.4 pounds of methane were introduced per hour (3.8 mois of chlorine per mol of methane). For each volume of reactants introduced, seven volumes of reaction product gases recycled from the photochemical chlorinator were added. The combined gases entered the chlorinator at 9, temperature of 258 C. In this photochemical chlorinator of the chlorine in the feed reacted with the methane. The eiuent gases from the photochernical chlorinator were then fed to the catalytic chlorinator under the same conditions and with substantially the same results as disclosed above in Example l.

Example 3 Into a system including two photochlorinators, 177 pounds (2.5 mols) of chlorine per hour and 10.5 pounds (0.66 mol) of methane per hour were fed'into the first chlorinator. In this first chlorinator the temperature was maintained at 258 C. by recycling effluent gas to the extent of 17.7 mols per hour, the said gases during recycling having been passed through an external cooler wherein the temperature was reduced to C. from whichcooler the gas liowed back to the same chlorinator. In this rst chlorinator the chlorine reacted at the rate of pounds per hour representing 76% of the net chlorine fed.

The non-recycled ei'luent gas after being cooled to 66 C. was then introduced into the second chlorinator wherein the heat of reaction raised the temperature of the gas to 263 C. In this second chlorinator the chlorine reacted at the rate of 24.4 pounds per hour representing 14% Yof the chlorine originally fed into the system. This additionalreaction led to a total chlorine conversion in the two chlorinators of 90%. The eliuent gas mixture from the second lchlorinator could be introduced into the catalytic chlorinator to carry the chlorination to completion, by following the procedure of Example l.

Example 4 -Y In the chlorinating system in the accompanying drawing a preferred procedure suggestedby various experimental runs involves introducing chlorine in a quantity of about 1200 pounds per hour with methane in the molar ratio V0f 35o-of the former to 1 of the latter into ,the rst photo-` chemical chlorinator lila together with four times their volume of reaction product recycle gases. The temperature in this reactor is maintained at about 300 C. A test of the effluent gases will show that about .50% of the chlorine has been converted. The eiuent gases from this rst reactor are then mixed with aboutan equal volume of reaction product recycle gases: and passed through the second photochemical Vreactor ib at substantially thesame ltemperature and .in such reactor the totalchlorine conversion will reach about 70%. The eiiiuent gases from the second chlorinator in passing through-'the third, fourth and fth photochemical chlorinators 10c, 10d and le at temperatures also maintained at about 300 C'. will leadto're'action product gases having about 9% of theoriginal chlorine in a free state.

rEhe eiuent gases'from the fth `plriotochemical chlorinator 40e when passed through the catalytic chlorinator under the conditions hereinbefore described Will produce chlorinated methane composed principally of carbon tetrachloridein a condition substantially ree'of chlorine.

The present invention can be operated` in photochemical and catalytic reactors and with cooling means other than those specically illustrated in the drawing. Apparatus of diierent construction and other sources ofy actiniclight may-be used.

The recirculation of the reaction product gases is a step the' usefulness of which is not restricted to the herein described combination photochcmical-catalytic halogenation process, for it may be used to advantage'in any direct halogenation procedure whether it be photochemical, catalytic or thermi-c or any combination of the same including photochemical chlorination followed by ther-mic chlorination and/or catalytic chlorination. This recirculation of the effluentl gases Without the separation of any of the constituents does not materially add to the complexity of the process, whereas the recirculation of any separated constituent of the reaction product 'gases disadvantageously complicates the operation- It should be understood that the invention is not limited to the raw materials and conditions of reaction specifically disclosed herein but that it extends to al1 equivalents which will occur to those skilled in the art upon consideration `of the claims appended hereto.

We claim:

1. In gaseous phase elevated temperature processes for the halogenation of hydrocarbonsv and their incompletely halogenated derivatives, the improvement which comprises passing the material to be halogenated and a halogen into a zone effecting reaction by photochemical catalysis solely wherein the majorpart of the halogen combines to form halogenated derivatives, and passing the eiliuent gases leaving said zone composed of unhalogenated material and halogen and the halogenated derivative through a zone containing a solid catalytic substanceA as the sole catalytic agent wherein combination of the remaining halogen occurs, thereby producing halogenated hydrocarbon eiiluent gases substantially free of halogen.

2. In a gaseous phase elevated temperature processes for the chlorination of hydrocarbons and their incompletely chlorinated derivatives, the'improvement which comprises passing the material to be chlorinated and chlorine into a zone effecting reaction by photochemical catalysis solely at a rapid rate which leaves a minor amount of unreacted chlorine in the eiuent gases containing unreacted material as well as the formed chlorinated derivative thereof, and passing the hot eiluent gases through a zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs, thereby producing chlorinated hydrocarbon eiliuent gases substantially free of chlorine.

3. A process for producing halogenated hydrocarbons from hydrocarbons and incompletely halogenated derivatives thereof Which comprises mixing the compound to be halogenated with a halogen, reacting the mixture in a zone eecting reaction by photochemical catalysis solely in a continuously ilowing gaseous stream of a rapidity which leaves a minor amount of unreacted halogen in the reaction product gases containing halogenated hydrocarbon and unreacted compounds, passing the reaction product gas mixture into a zone containing a solid catalytic substance as the sole catalytic agent. forming additional halogenated hydrocarbons in said zone by reactions involving the remaining halogen, thereby producing halogenated hydrocarbon eiiluent gases substantially free of halogen, and taking up excess exothermic heat developed in the catalyst by transfer to the reaction gases from both the photochemical and catalytic reactions whereby decomposition of the halogenated hydrocarbons obtained is avoided.

4. A process for producingchlorinated hydrocarbons from hydrocarbons and their incompletely chlorinated derivatives which comprises continuously passing a gaseous mixture of the compound to be chlorinated together with chlorine through a zone effecting reaction by photochemical catalysis solely at a rapid rate which produces chlorinated hydrocarbon reaction product gases containing not more than fifteen per cent of the original free chlorine, passing the eiiluent gases containing unchanged reactants through a zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs thereby producing chlorinated hydrocarbon eiuent gases substantially free of chlorine.

5. A process for producing chlorinated hydrocarbons from hydrocarbons andY their incompletely chlorinated derivatives which comprises exposing a continuously owing gaseous stream of the compound to be chlorinated together with chlorine into a zone eiecting reaction by photochemical catalysis solely thereby reacting the gases at a temperature of from 'about A100" C. to about 300 C., regulating the rate of i'low at a rapidity which leaves in the eiiluent gases a small amount of chlorine not in excess of of the original amount, passing the efliuent gases containing unchanged reactants through a @one containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs thereby producing chlorinated hydrocarbon eiiluent gases substantially free of chlorine.

10 6. A process for producing chlorinated hydrocarbons from hydrocarbons and their incompletely chlorinated derivativeswhich comprises, continuously passing a gaseous mixture of the 'compound "to be chlorinated and chlorine together with recycle gases hereinafter defined, through a zone eiecting reaction by photochemical catalysis solely at a rapid rate which produces chlorinated hydrocarbon reaction product gases containing a minor amount of the initial chlorine, dividing the said reaction product gases into two parts, cooling one part of said gases and recycling the same into the said photochemical reaction zone as hereinbefore described, the said part recycled through the said zone being in an amount which takes up excess heat and prevents decomposition of chlorinated hydrocarbons in the said zone, passing the remaining part of the reaction product gases containing unchanged reactants through a zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs, thereby producing chlorinated hydrocarbon eiiiuent gases substantially free of chlorine.

7. A gaseous phase, elevated temperature process for the halogenation of hydrocarbons and their incompletely halogenated derivatives, which comprises passing the compound to be halogenated and the halogen first through a zone effecting reaction by photochemical catalysis solely wherein the major part of the halogen is reacted, passing the reaction product gases containing the remaining reactants through a Zone containing a solid catalytic substance as the sole catalytic agent to accomplish completion of the reaction of the halogen whereby halogenated hydrocarbon eiiiuent gases substantially free of halogen are obtained, controlling the temperature in the photochemical reaction zone by recirculating part of the undivided reaction product gaseous mixture and cooling the same before said part is introduced into the photochemical reaction zone together with the reactants.

8. In a gaseous phase, elevated temperature process for the halogenation of hydrocarbons and their incompletely halogenated derivatives, the improvement which comprises passing the material to be halogenated and a halogen into and through a series of zones eiecting reaction by photochemical catalysis solely at a rapid rate which leaves a minor amount of unreacted halogenin the eluent gases of the last reaction zone, passing the eluent gases containing the unreacted material together with the halogenated hydrocarbons formed through a zone containing a solid catalytic substance as the sole catalytic agent wherein a combination of the remaining halogen occurs, vthereby producing halogenated hydrocarbon eiliuent gases substantially free of halogen.

9. A process for producing' chloromethanes from methane which comprises continuously passing a gaseous mixture of methane and chlorine successively Athrough a series of zones eiecting reaction by photochemical catalysis solely at a rapid rate which produces chloromethane eiiiuent gases containing not more than 15% of the original free chlorine, passing the eiiluent gases containing unchanged reactants together with chloromethanes through a catalytic reaction zone containing a solid catalytic substance wherein as the sole catalytic agent combination of the remaining chlorine occurs, thereby pro- 11 ducing chloromethanes in a condition substantially free of chlorine.

10. A process for producing chlorinated hydrocarbons from hydrocarbons and their incompletely chlorinated derivatives which comprises continuously passing a gaseous mixture of the material to be chlorinated and chlorine together with recycle gases hereinafter defined through a series of zones effecting reaction by photochemical catalysis solely at a rapid rate which produces chlorinated hydrocarbon reaction product gases containing not more than of the initial chlorine in a free state, dividing the said reaction product gases leaving the rst zone of said series into two streams, cooling one stream of said gases and recycling the same into said first zone as hereinbefore described, then passing the second stream of the reaction product gases after leaving the last zone of said series through a catalytic reaction zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs, thereby producing chlorinated hydrocarbon effluent gases substantially free of chlorine.

11. A process for producing chloromethanes from methane which comprises continuously passing methane and chlorine together with recycle gases hereinafter defined through a series of ve zones effecting reaction by photochemical catalysis solely at a rapid rate which produces chloromethanes containing a minor amount of the initial chlorine, dividing the effluent gases leaving the rst zone of the series into two streams, cooling one stream of said gases and recycling the same into the said rst Zone as hereinbefore described, passing the remaining stream of eliluent gases containing chloromethane gases, unchanged methane and chlorine after they leave the fth zone of said series through a zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs, thereby producing chloromethanes in a condition substantially free of chlorine.

12. A process for the chlorination of hydrocarbons having up to rive carbon atoms and their irl-completely chlorinated derivatives which comprises, passing vapors oi the material to be chlorinated and chlorine into a zone effecting reaction by photochemical catalysis solely at a rapid rate which produces chlorinated hydrocarbon reaction product gases containing part of the original free chlorine but not more than 15% thereof, passing the effluent gases containing unchanged reactants through a reaction zone containing a solid catalytic substance, as the sole `catalytic agent wherein combination of the remaining chlorine occurs, thereby producing chlorinated hydrocarbon eiiluent gases substantially free of chlorine.

13. A process for the halogenation of hydrocarbons having up to three carbon atoms and their incompletely halogenated derivatives in the gaseous phase at elevated temperatures which comprises, passing vapors of the material to be halogenated and a halogen into a zone effecting reaction by photochemical catalysis solely wherein a larger part of the halogen is combined to form halogenated derivatives, and passing the 12 effluent gases containing not more than 15% of the original free halogen through a reaction yZone containing a solid catalytic substance 'as the sole catalytic agent wherein combination of the' remaining halogen occurs, thereby producing eiiiuent gases substantially free of halogen containing the halogenated hydrocarbon of not more than three carbon atoms.

14. A process for the chlorination of hydrocarbons having up to three carbon atoms and their incompletely chlorinated derivatives in the gaseous phase at elevated temperatures which comprises, passing the material to be chlorinated and chlorine into and through a series of zones effecting reaction by photochemical catalysis solely at a rapid rate which leaves a minor amount of unreacted chlorine in the eluent gases of the last reaction zone, passing the eiluent gases containing unreacted hydrocarbon material and the remaining chlorine together with the chlorinated hydrocarbons formed through a reaction zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs, thereby producing effluent gases substantially free of halogen composed of chlorinated hydrocarbons having up to three carbon atoms.

15. A process for producing chlorinated hydrocarbons from hydrocarbons having up to three carbon atoms and their incompletely chlorinated derivatives in the vapor phase at elevated temperatures which comprises, continuously passing a gaseous mixture of the material to be chlorinated and chlorine together with recycle gases hereinafter defined through a series of zones electing reaction by photochemical catalysis solely which produces in the efiluent gases of the last of the reaction Zones chlorinated hydrocarbon reaction product gases containing part of the initial chlorine in a freestate but not more than 15% of the original amount, dividing the eluent reaction product gases of the rst zone of the series into two streams, cooling one stream of said gases and recycling the same into said first zone as hereinbefore described, then passing the second stream of the reaction product gases of said eiuent gases through a zone containing a solid catalytic substance as the sole catalytic agent wherein combination of the remaining chlorine occurs, thereby producing eiliuent gases substantially free of chlorine composed of chlorinated hydrocarbons having up to three carbon atoms.

JOHN A. PIANFETTI. ROBERT W. TIMMERNAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

1. IN GASEOUS PHASE ELEVATED TEMPERATURE PROCESSES FOR THE HALOGENATION OF HYDROCARBONS AND THEIR INCOMPLETELY HALOGENATED DERIVATIVES, THE IMPROVEMENT WHICH COMPRISES PASSING THE MATERIAL TO BE HALOGENATED AND A HALOGEN INTO A ZONE EFFECTING REACTION BY PHOTECHEMICAL CATALYSIS SOLELY WHEREIN THE MAJOR PART OF THE HALOGEN COMBINES TO FORM HALOGENATED DERIVATIVES, AND PASSING THE EFFLUENT GASES LEAVING SAID ZONE COMPOSED OF UNHALOGENATED MATERIAL AND HALOGEN AND THE HALOGENATED DERIVATIVE THROUGH A ZONE CONTAINING A SOLID CATALYTIC SUBSTANCES AS THE SOLE CATALYTIC AGENT WHEREIN COMBINATION OF THE REMAINING HALOGEN OCCURS, THEREBY PRODUCING HALOGENATED HYDROCARBON EFFLUENT GASES SUBSTANTIALLY FREE OF HALOGEN. 